class Node():
    def __init__(self,value):
        self.value = value
        self.next = None


#头插法
class List:
    def __init__(self):
        #头节点
        self.head = Node(-1)
    #前插法创建单链表
    def insert_before(self,data):
        for i in data:
            node = Node(i)#创建新节点
            #判断头节点的下一个节点是否为空
            if self.head.next is None:#如果为空，则将新节点加入到next
                self.head.next = node
            else:
                node.next = self.head.next#将头节点的下一个节点加入到当前节点的next
                self.head.next = node
    #尾插法创建单链表
    def insert_tail(self,data):
        tail=self.head.next
        for i in data:
            node=Node(i)
            if tail is None:
                self.head.next = node
                tail = node
            else:
                tail.next = node
                tail=node

    #删除链表中重复元素
    def clear_repetition(self):
        cur = self.head
        while cur:
            while cur.next and cur.value==cur.next.value:
                cur.next=cur.next.next
            cur=cur.next

    #在第i个节点前插入值为value的节点
    def list_element_add(self,i,value):
        node_new = Node(value)#创建新节点
        index = 0
        node = self.head.next
        while node:#找位置
            index = index + 1
            if index == i - 1:
                break
            node=node.next
        if node is None:
            return False
        node_new.next = node.next#插入节点
        node.next = node_new


                